The present invention relates to a surface-treating agent for a metal can and a method for treating a metal can surface, which are applied to a metal can surface to diminish friction on the surface and thereby, bring about a surface condition preferable to production of the can. In detail, the invention relates to a surface-treating agent for a metal can and a method for treating a metal can surface, which diminish friction on an outside surface of the metal can, especially an aluminum can, without giving a bad influence on attachability of paint or lacquer and thereby, which can improve mobility on a conveyor.
The metal can is used as a vessel for various products and, especially, the aluminum can is widely used as the most common metal can. Hereinafter, the aluminum can is cited as an example and explained.
The aluminum can is washed by an acid cleaner and the like to remove fine aluminum powder and other contaminators after the can main body is produced. However, recently, because of environmental problems and because an acid liquid remaining on the can after washing by acid gives a bad influence on the smell of can contents, removal of fine powder and other contaminators by washing by alkali has been desired.
However, if the washing by alkali is carried out to remove fine powder in an inside of the aluminum can, an outside surface of the can becomes coarse in such condition and the can does not smoothly move on a belt conveyor in a process to fill the can contents, a process to print the can surface and other processes, so that the following problems occur: the mis-supply of cans, productivity decease, increase in the can-losing ratio, and the like.
Therefore, it is desired to diminish the friction on an outside surface of the can without giving a bad influence on attachability of paint, lacquer and the like to the outside can surface.
Japanese Official Patent Provisional Publication (Kokai) No. showa 64-85292 describes phosphoric acid esters, ethylene oxide adducts of fatty acids, ethylene oxide adducts of higher alcohols and the like as surface-treating agents for a metal can, to solve the above-mentioned problems.
However, since the aluminum can and the like are often used for food articles and since the above-mentioned compounds have a problem in safety to the human body, the compounds cannot be used as a widely used surface-treating agent for a metal can.